Nanotechnology encompasses a set of tools and methods that scientists use to see, measure, and precisely control matter, sometimes moving just one atom at a time. Nanotechnology generally involves but is not limited to development and use of materials or devices with structures of the size 100 nanometers or smaller. Nanotechnology may for example use “bottom-up” approaches, in which materials and devices are built from molecular components, and “top-down” approaches, in which nano-objects are constructed from larger entities.
A number of physical phenomena become pronounced as the size of a system decreases, including statistical mechanical effects and quantum mechanical effects (for example, the “quantum size effect,” where greatly reducing particle size alters the electronic properties of solids). In addition, a number of physical (mechanical, electrical, optical, etc.) properties change in a nanoscale system as compared to macroscopic systems. Materials reduced to the nanoscale can show different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent (copper), stable materials become combustible (aluminum), solids turn into liquids at room temperature (gold), and insulators become conductors (silicon). A material such as gold, which is chemically inert at normal scales, can serve as a potent chemical catalyst at nanoscales.
In nanotechnology, a particle may be defined as a small object that behaves as a whole unit in terms of its transport and properties. Nanoparticles may or may not exhibit size-related properties that differ significantly from those observed in fine particles or bulk materials. One type of nanoparticle is a nanocluster, which may exhibit but is not limited to dimensions between 1 and 10 nanometers and a narrow size distribution. Nanocluster shapes include nanospheres, nanorods, and nanocups, among many others.
Oblong nanorods have become a readily available commodity. Metal nanorods can be made in the laboratory by aging Cadmium Sulfide (CdS) particles, or by the action of the bacteria shewanella oneidensis. They are also commercially available in gold, permalloy, nickel, zinc oxide, and a number of other conductive materials. Nanorods have a range of potential uses, including display technologies, microelectromechanical systems, optical, sensing, solar cells, magnetic and electronic device applications.